This invention relates to a process for disposing of waste carbon fibers in an economical and relatively safe manner.
In the search for high performance materials, considerable interest has been focused upon carbon fibers. Industrial high performance materials of the future are projected to make substantial utilization of fiber reinforced composites, and carbon fibers theoretically have among the best properties of any fiber for use as a high strength reinforcement. Among these desirable properties are corrosion- and high temperature-resistance, low density, high tensile strength, and high modulus. Graphite is one of the very few known materials whose tensile strength increases with temperature. Uses for carbon fiber reinforced composites include recreational equipment, aerospace structural components, rocket motor casings, deep-submergence vessels, and ablative materials for heat shields on re-entry vehicles.
While these fibers are relatively safe in their intact form, and particularly so if they are embedded in a resin, disposing of carbon fibers is a problem. When disintegrated as by incineration very fine, lightweight fibers may result, and, due to their small size, are readily released into the environment. These airborne fibers may pose an electrical hazard and may cause shorts or arcing in electrical equipment, and subsequent power failures or fires.
British Patent Application No. 2065707A relates to a process for facilitating safe incineration of carbon fibers wherein the fibers are treated by electrocoating or electrodeposition of materials such as phosphorous compounds, titanates, polyimides, polyquinoxalines, nitriles, or boric acid. This process imparts a high electrical resistance to the carbon fibers. However, this process of course requires a pre-treatment which may be costly and time consuming, and may also hinder the compatibility of the fibers with a resinous matrix.
U.S. Pat. Nos. 3,859,187 and 3,894,884, and British Pat. Nos. 1,238,308 and 1,257,022, and German Offenlegungsschrift No. 2,048,916 disclose surface modification of carbon fibers by use of a sodium hypochlorite solution. However, this treatment is intended to facilitate enhanced adhesion between the intact fiber and a resinous matrix. For example, U.S. Pat. No. 3,894,884 to Druin et al. discloses treatment of carbon fibers for about 1 to 60 minutes with an aqueous solution of sodium hypochlorite at a concentration of about 3 to 7 percent by weight active chlorine, at a temperature of between 20.degree. and 35.degree. C., to effect improved fiber-resin adhesion.
It is an object of this invention to provide a method for safely disposing of carbon fibers.
It is a further object of this invention to provide a method for disposing of carbon fibers which is relatively rapid and inexpensive.
It is a further object of the invention to provide a method for disposing of carbon fibers which is simple and requires no pre-treatment of the fibers.
These and other objects, as well as the scope, nature, and utilization of the invention will be apparent from the following detailed description and appended claims.